<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8" />
    <title>4.字符串的includes方法</title>
  </head>
  <body>
    <script type="text/javascript" >
      let str = 'hello'

      // str.includes('a') //false
      // str.includes('') //true

      // let x = str.indexOf('')
      // console.log(x)

    </script>
  </body>
</html>